1. Field of the Invention
The present invention relates to a method of operating a refrigerating machine in a refrigerating and air-conditioning system which can be made use of in buildings and warehouses for air-conditioning and refrigeration.
2. Description of the Prior Art
Usually, in a refrigerating and air-conditioning system, there is employed a refrigerator or refrigerating machine having a capacity which is smaller than the maximum value of the load to be conditioned by the system, with a view to decreasing cost for equipment and maintenance as well as reducing contract demand. To this end, the refrigerating machine or refrigerator is generally sperated in a manner illustrated in FIGS. 1, 2 and 3, by way of example, wherein FIG. 1 is a view to illustrate variation in the load of the refrigerating and air-conditioning system during a period from the start of the air-conditioning operation to the end thereof, and FIGS. 2 and 3 illustrate variations in the quantity of accumulated heat and output power of the refrigerating machine, respectively, during operation of the refrigerating machine. It is obvious that the load Q.sub.L is effective over a time span between the the initiation of the air-conditioning operation at a time point t.sub.S1 and the termination thereof at a time point t.sub.S2. As can be seen from FIG. 1, since the maximum value of the load Q.sub.L exceeds the maximum value Q.sub.R MAX of the output Q.sub.L of the refrigerating machine, energy for the air-conditioning will become insufficient by an amount which corresponds to a sum (S.sub.1 +S.sub.3 -S.sub.2) of integrals S.sub.1, S.sub.2 and S.sub.3 shown in FIG. 1. In an effort to evade such shortage, it is common in practice to start the operation of the refrigerating machine at a time point t.sub.S1 ' which is earlier than the time point t.sub.S1, as is illustrated in FIGS. 2 and 3, to thereby accumulate energy for the air-conditioning in a heat storage tank by an amount as predicted. Thus, the refrigerating machine is operated in a manner illustrated in FIG. 3. In this connection, it will be noted that selection of a refrigerating machine the maximum output Q.sub.R MAX of which is relatively low for the purpose of reducing the equipment cost will in turn involve the necessity for installing a heat storage tank of a correspondingly increased capacity. Inversely, when a heat storage tank of a relatively small capacity is used, a refrigerating machine having a correspondingly increased maximum output Q.sub.R MAX has to be employed, which means of course a corresponding increase in the equipment cost. under the circumstance, the refrigerating machine having an appropriate maximum output Q.sub.R MAX is in practice selected as a compromise between the equipment cost and the capacity of the heat storage tank. In the case of the operating method illustrated in FIGS. 1, 2 and 3, it should however be noted that the refrigerating machine is always under operation during the time span in which the load to be conditioned is alive, as the result of which the refrigerating machine has to be operated at the maximum output level whenever the load is at maximum. By the way, in the cooling operation made of the refrigerating and air-conditioning system, the time period during which the air-conditioning load is high will coincide with a time period in which an ambient wet-bulb temperature is high, which means that the refrigerating machine is put into operation when the temperature of cooling water of the refrigerating machine is high, i.e. when the coefficient of performance of the refrigerating machine is low. Thus, the conventional operating method of the refrigerating machine is disadvantageous in that the operating cost for the refrigerating and air-conditioning system is considerably increased.
A Japanese patent publication No. 46501/'72 discloses another type of refrigerating system in which the refrigerating machine is operated at night to accumulate a predetermined amount of heat and, at the same time, an amount of heat to be used on that day is predicted. When the predictive heat amount is larger than the accumulated heat amount, the refrigerating machine is operated by using surplus power in the day time to compensate for the insufficient amount of the heat.